1. Technical Field
The present invention relates to a light source device and an image display device, and particularly to technology of a light source device used in combination with a spatial light modulator.
2. Related Art
Recently, it has been proposed that a solid light emitting element is used in a light source device of a projector. A light emitting diode (hereinafter referred to as “LED”) that is the solid light emitting element is characterized by being ultra small, ultra light, and long in life. Further, the LED for large output is in a remarkably advanced stage of development and improvement, so that application of the LED to use for illumination is enlarging. Therefore, it is expected that the LED is used as a light source of a projector, and particularly as a light source of a small-sized and bright projector. The more efficiently light from a light emitting part can be utilized, the brighter image can be obtained. Technology for utilizing efficiently the light from the light emitting part has been proposed in, for example, JP-A-2000-221499 and JP-A-2003-57445.
In the technologies proposed in JP-A-2000-221499 and JP-A-2003-57445, polarized light in a specified vibrating direction is supplied to a spatial light modulator. As the spatial light modulator which modulates the polarized light in the specified vibrating direction, there is a liquid crystal type spatial light modulator. A tilt mirror device used as the spatial light modulator of a projector except the liquid crystal type spatial light modulator modulates incident light regardless of a polarization state. Therefore, in the case that the tilt mirror device is used in place of the liquid crystal type spatial light modulator, it is thought that the constitution for polarization conversion is omitted from the constitution disclosed in JP-A-2000-221499 and JP-A-2003-57445.
In the case that the LED that is being developed is used in the projector, plural LED's must be used in order to obtain a bright image. In the case that plural LED's are used, according to the technologies in JP-A-2000-221499 and JP-A-2003-57445, the LED's are arranged in the shape of an array. In the case that the plural LED's are arranged in the shape of an array, the larger the number of the LED's is, the larger the region in which the LED's are arranged becomes. Further, in the projector, in an optical system including the light source device and the spatial light modulator, spatial extent in which luminous flux effectively handled exists can be expressed by the product of the area and the solid angle (Etendue, Geometrical Extent). This product of the area and the solid angle is stored in the optical system. From this point, it is thought that the use of the plural LED's increases the spatial extent of the luminous flux that is incident on the spatial light modulator.
On the other hand, a taking-in angle of the light which the spatial light modulator can effectively modulate has a limit. Therefore, the larger the spatial extent of the luminous flux which is incident on the spatial light modulator is, the more difficult it is to use the light from the light source device effectively. Therefore, even in the case that the technologies disclosed in JP-A-2000-221499 and JP-A-2003-57445 are used, there is a case in which the light cannot be efficiently utilized. Particularly, impossibility of the efficient utilization of the light from the light emitting part is a problem, because there is a case in which a bright image cannot be obtained even when plural light emitting parts are used.